The present invention relates to a voltage control system for vehicles, which is capable of controlling the generation of power of an AC generator installed in a vehicle and also giving a warning that the power generation is not normal or faulty.
A known voltage control system of the above type is shown in FIG. 1 of the accompanying drawings. In the case of this system, a voltage regulator circuit 200 includes a path comprising a resistor 208 and a diode 209 so that when a break occurs in a charging line l.sub.1 or a voltage detection line l.sub.2, the power generation control is accomplished in accordance with the voltage generated from an auxiliary rectifier 4, thus preventing the generator from becoming uncontrolled. Also an energizing resistor 71 is connected to an "L" terminal so that when the power generation is stopped due to a break in the energizing circuit, a lamp 9 is turned on through the resistor 71 to give a warning.
However, this system is disadvantageous in that while the generator can be prevented from becoming uncontrolled upon occurrence of a break in the charging line l.sub.1 or the voltage detection line l.sub.2, it is impossible to indicate the occurrence of such fault and particularly in the case of a break in the charging line l.sub.1 the driver cannot become aware of the break until the battery runs down. There is another disadvantage in that the voltage regulator circuit 200 is supplied with power from the auxiliary rectifier 4 so that due to the presence of the break detecting resistor 71, during the initial excitation period or when the power generation is faulty, the voltage at the "L" terminal decreases considerably as compared with the battery voltage with the resulting decrease in the supply voltage to the voltage regulator circuit 200, thereby causing in certain circumstances the operation of its circuit component (an output transistor 201 in this case) to become unstable.